1. Technical Field
Aspects of the present invention relate to an image reading device which reads an image from a document.
2. Related Art
Image reading devices having a photoelectric conversion device which reads an image from a document and outputs an analog signal corresponding to the image, and an A-D converter which converts the analog signal outputted by the photoelectric conversion device into a digital signal have been proposed. In the image reading device configured as described above, various types of processing can be executed by converting the analog signal outputted by the photoelectric conversion device into the digital signal via the A-D converter.
When the photoelectric conversion device starts to output the analog signal, the analog signal varies for a certain delay time and thereafter moves into a stable period. Therefore, a possibility, that a value of the acquired analog signal varies due to shift of the acquiring timing of the analog signal which is converted to the digital signal by the A-D converter, arises.
On the other hand, a technique of using a spread spectrum clock obtained by spreading a reference clock having a constant frequency has been proposed for EMI (Electromagnetic Immunity) provisions of electronic appliances accommodating the above described image reading device. However, if the acquiring timing of the analog signal is defined based on the spread spectrum clock, the acquiring timing shifts on a time axis depending on the current frequency of the spread spectrum clock. Therefore, a possibility that the value of the acquired analog signal varies arises.
In such a case, it is possible to acquire the output of the photoelectric conversion device at the timing delayed by a predetermined delay time with an analog delay-unit which defines the predetermined delay time independently of the spread spectrum clock, from the start timing of the output of the analog signal from the photoelectric conversion device.